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Re: Can twisted wire replace shielded wire?

F

Floyd L. Davidson

Jan 1, 1970
0
Phil Allison said:
"Floyd L. Davidson"

You clipped off the rest of that line, which was:

Hilarious. Do you know what amplitude distortion is?
** You are nothing but a lying, posturing fool - Davidson.

The moose in Alaska can out think a bullshit artist of your ilk.

You don't know what amplitude distortion is!
 
F

Floyd L. Davidson

Jan 1, 1970
0
Phil Allison said:
"Floyd L. Davidson"


** The fact that a co-ax cable ( like RG58) is insensitive to low frequency
magnetic fields readily demonstrated.

Aluminum and copper do not make good shielding material for low frequency
magnetic fields. Steel does, and in critical situations coax should be
placed inside a steel conduit. Likewise AC power distribution should also
be run inside steel conduit.
At least 40dB less sensitive than a non twisted pair ( figure 8) cable.

Do you have a cite for that and for a comparison to twisted pair?
 
P

Phil Allison

Jan 1, 1970
0
"Floyd L. Davidson"


** You are nothing but a lying, posturing ass - Davidson.

The moose in Alaska can out think a fuckwit bullshit artist of your ilk.




......... Phil
 
P

Phil Allison

Jan 1, 1970
0
"Floyd L. Davidson"
Aluminum and copper do not make good shielding material for low frequency
magnetic fields.


** Piss off - cable tugger idiot.




........... Phil
 
F

Floyd L. Davidson

Jan 1, 1970
0
Jasen Betts said:
["Followup-To:" header set to sci.electronics.basics.]
Twisting wires helps reduce noise induced from ambient H fields. If you

Of course that is true, but it is true for exactly the reasons that were
stated for why the twist maintains balance: it equalizes proximity.

The exact same noise reduction is available in non-twisted pair if there
is no variation in proximity (i.e., if proximity is to an object that is
a vastly huge distance, the difference between proximity to one wire is
not significantly different than to the other wire). In practice cable
is installed where there are other objects, and sources for interfering
fields are not infinitely distant, so the twists maintain equal proximity
and thus balance.

Keeping in mind that typical CMRR for 60 Hz is something like 90
dB.

But that is in fact why microphone cables are often STP. And
instrument data in electrically harsh environments is also
commonly STP. As opposed to typical telephone cable at a customer
location. Note however that a great deal of the cable used at
a telco central office is multi-pair with a shield. And of course
virtually all outside plant feeder cables are also shielded (just not
each individual pair, hence it is not "STP").
transformers typically have very a high CMRR. this may be whay they are used
in network cards.

Those are "specially wound" transformers too. They have bifilar
windings to maintain balance, and thus CMRR.
taken from an old 10Mb/s card.

1nF
2KV
_______ || ______________\
_) || (_ /
from _) || (____||___ to RJ12
driver _) || (_ || | socket
chip_____) || (_________|____\
|| | /
___L__
/////

I think the capacitor is to reduce the amount of CM noise
transferred capacitatively through the transformer.

AIUI transformers are also often used for balanced microphone leads.

---------+ +------------->
| |
o---+ o || o +---o
} | } || { | {
} | } || { | {
} | } || { | {
| | | || | | |
--+ +--+ +--+ +------>
|
-----
 
R

RHF

Jan 1, 1970
0
For One and All,

Twin (Paired) Flat-Wires as Noise Cancelling Wire Antenna Elements
http://groups.yahoo.com/group/Shortwave-SWL-Antenna/message/6712

IMHO - Twin (Paired) Flat-Wires [TPFW] (the Un-Twisted kind) can be
put to good use as "Receive Only" Shortwave Listener (SWL) Antennas.

Two very common TPFW Wires to used as Wire Antenna Elements :
Common Speaker Wire and Common 300 Ohm Twin Lead can be
employed as a Low-Noise Antenna Element in several ways :

1. Replace the UnUn and Single Wire of a Random Wire, Inverted
"L" Antenna, Sloper with either of these TPFW Wires. Use a Balun
and Coax Cable and wire one of the two TPFW Wires to one side
of the Balun's Balanced Input and the other Wire to the other side
of the Balun's Balanced Input. At the Far-End of the Two Common
Wires; strip and twist the Wires together and Seal the Connection.

2. With a Dipole or other Balanced Antenna replace the Single Wire
with either of these TPFW Wires. Wire them to the Balun like a
Folded Dipole that is Tapped in the Center of One of the TPFW Wires
with both the End-Wires on each side; strip and twist together and
Seal the Connection.

3. A Vertical Wire Antenna for limited-space (no-space) when
nothing else can be done. Use a Balun and Coax Cable and wire
one of the two TPFW Wires to one side of the Balun's Balanced
Input and the other TPFW Wire to the other side of the Balun's
Balanced Input. At the Top-Far-End of the TPFW Wires; strip
and twist the Wires together and Seal the Connection.

All of the Above can be maked using TV 'type' Parts :

* 300 Ohm Twin Lead {or Speaker Wire} as the Twin Parallel
(Noise Cancelling) Flat Wire Antenna Element.

* TV 300 Ohm Matching Transformer (Balun)

* RG6 or RG59 Coax Cable with "F" Connectors.

NOTE - None of these are great Shortwave Listening (SWL) Antennas :
But they are made of easy to find common TV 'type' parts to build
them and putting them together is simple and understandable for
most Shortwave Listeners (SWL). An Easy-to-Do First Antenna :eek:)

All are WELCOME and "Invited to Join" the
Shortwave Listener (SWL) Antenna eGroup on YAHOO !
<http://groups.yahoo.com/group/Shortwave-SWL-Antenna/>
SWL ANTENNAS GROUP => http://tinyurl.com/an6tw
 
P

Phil Allison

Jan 1, 1970
0
"Floyd L. Davidson"
Paul Hovnanian P.E.
Of course that is true, but it is true for exactly the reasons that were
stated for why the twist maintains balance: it equalizes proximity.


** Moose Stoopid and plain wrong.

It creates opposing polarity loops.

The exact same noise reduction is available in non-twisted pair if there
is no variation in proximity


** Moose Stoopid and plain wrong.

The included loop area of the pair must always be minimised.

Take no notice of this " Floyd " idiot cable guy wanker.



.......... Phil
 
P

Phil Allison

Jan 1, 1970
0
Jasen Betts said:
AIUI transformers are also often used for balanced microphone leads.


** Where a low impedance mic input uses a transformer it almost invariably
there for impedance matching.

The pre-amp's electronics may use an audio op-amp that is non ideal for low
a impedance sources or even a vacuum tube - in which case the input
transformer increases the impedance by 25 to 100 times and greatly improves
the signal to noise ratio.

It is rare for a mic cable to suffer from significant CM noise injection -
the real problem is *differential mode* injection of hum voltage from
nearby AC power cables, particularly ones carrying chopped current waveforms
from lighting dimmers.

A special kind of 4 wire twisted ( platted really) mic cable was developed
years ago to solve this annoyance in TV studios etc - called "Star Quad "
mic cable.



......... Phil
 
C

Cliff

Jan 1, 1970
0
Cliff wrote:





Good god a'mighty, which comic book did you read that piece of crap in.
You have just written the most compacted wad of horseshit I've ever
read with respect to transmission lines. Get a book, learn some theory
concerning (cables, open wire or co-axial etc.). Then, take a stab at
explaining things.

Care to explain it?

The fishing seems just fine <G>.
 
C

Cliff

Jan 1, 1970
0
No, but they're all shorted, making the effective length of the
shield less than the length of any of its individual conductors.

There might be an oxide finish that's not all that conductive
on those fine strands, the conduction points between strands
might be many small ones & of high resistance each or the
various possible conduction paths might zig-zag quite a bit,
adding length ... <G>.
 
J

John Fields

Jan 1, 1970
0
There might be an oxide finish that's not all that conductive
on those fine strands, the conduction points between strands
might be many small ones & of high resistance each or the
various possible conduction paths might zig-zag quite a bit,
adding length... <G>.
 
J

Jeff Lowe

Jan 1, 1970
0
Cliff said:
There might be an oxide finish that's not all that conductive
on those fine strands, the conduction points between strands
might be many small ones & of high resistance each or the
various possible conduction paths might zig-zag quite a bit,
adding length ... <G>.

Yep, and there might be quantum level black holes which might act as
continuum tranfunctioners. This might cause a localized distortion of
space-time which might cause the many zig-zags to have an effective path
length shorter than the center conductor.
 
G

Gary

Jan 1, 1970
0
Floyd L. Davidson wrote:


All of the above is equally true for twisted pair transmission
lines. Note however that there will *not* be "a lot of loss"
from mixing 50 and 75 ohm coax. It will actually be a very
small loss. (There are other factors that are much more
significant, but that gets more complicated than I'm going to
get in this article. Certainly if someone wants to discuss it,
we can and there will probably be a number of people who can
describe it in detail.)


I think most of you people are somewhat confused when dealing with the
characteristics of transmission lines of all types. For example, the
mixing of impedances as indicated above results in a "return loss" or
reflection loss. There also ohmic losses in transmission lines as well
as dielectric losses. Impedance is a constant characteristic of a
coaxial transmission, not a variable. It is a fixed quantity and is
calculated in the following manner.

Characteristic Impedance of a co-axial transmission line whose
dielectric material is air..

Example:

d1= the inside diameter of the outer conductor = 3"
d2= the outside diameter of the inner conductor=1.5"
e=1= dielectric constant of "air" (changes according to the
dielectric material used)

Z = 138/sqrt(e)x(log(d1/d2))
Z = 138/sqrt(1)x(log(3/1.5))
=41.54 Ohms

This co-axial transmission line has a characteristic impedance of 41.54 Ohms

Likewise, dielectric losses, ohmic losses and overall attenuation (which
all vary with frequency and line size) may be quantified through
calculation. Transmission lines are not devices that can be properly
evaluated through observation and/or measurement, their characteristics
are too complex.
Their sole purpose in life is to efficiently transfer energy from
generator to load. This is accomplished by having both the generator
and load impedances equal to the characteristic impedance of the
transmission line.

So, enough of the crap such as, "the wires in the shield are longer than
the center conductor. Therefore the outer conductor is longer than the
inner conductor". Keerist, that's even crummy observation.

Read a textbook for cripe's sake.

<snip>



--
Regards,
Gary

I know not with what weapons World War III will be fought,
but World War IV will be fought with sticks and stones.

Albert Einstein
 
D

David

Jan 1, 1970
0
I think most of you people are somewhat confused when dealing with the
characteristics of transmission lines of all types. For example, the
mixing of impedances as indicated above results in a "return loss" or
reflection loss. There also ohmic losses in transmission lines as well
as dielectric losses. Impedance is a constant characteristic of a
coaxial transmission, not a variable. It is a fixed quantity and is
calculated in the following manner.
Characteristic impedance and DC resistance are the same if the line is
infinitely long and unterminated.
 
G

Gary

Jan 1, 1970
0
David wrote:

Characteristic impedance and DC resistance are the same if the line is
infinitely long and unterminated.


Bullshit.



--
Regards,
Gary

I know not with what weapons World War III will be fought,
but World War IV will be fought with sticks and stones.

Albert Einstein
 
C

Cliff

Jan 1, 1970
0
Its effective length will still be less than that of an individual
wire in the braid. :)

So the longer conductors are not shorter after all? How long
do you suppose that they are compared to the central conductor ???
Now, about the speed of light in those conductors ... a lead or
a lag between the signal's phases?
 
C

Cliff

Jan 1, 1970
0
Yep, and there might be quantum level black holes which might act as
continuum tranfunctioners. This might cause a localized distortion of
space-time which might cause the many zig-zags to have an effective path
length shorter than the center conductor.

Where's Shu when we need her ???
 
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